How to minus columns in creating Measure

[ndmalam]

I have a table which contains the purchase data of two years i e 2020 and 2020.
Now i created a pivot table in which i want to show "item", "Rate of "year1", "year2" and then a column showing difference of rate, i.e "year1-year2".
By Now in my pivot table, Rows contain "Item", Values contain "Rate" and Columns section contain "Date(year) "
I am trying to create a Measure that shiws the result of colum lable 2020-2021.
Please help. Best regards.